Tried everything and cannot lose weight...what is wrong with me?

Never had a weight problem my whole life. Prior to this problem walked daily or did some type of exercise for 30 minutes, but nothing intense. Petite and always was around 100 pounds. First child dropped weight within weeks, second pregnancy had twins 10 weeks early. Weight did not drop off so Started restricting to under 1200 cal and started exercising  a lot more and actually gained weight. That was 5 years ago. I have tried everything. I started an exercise routine like i never had before and that only caused me to get bulky and gain more weight. Started running, weights, cycling, intervals, even ran a marathon, switched up routines, tried 5-6 miny meals sticking to 1200 calories and have not lost any weight. Had a blood panel and everything was fine. I am at the point the last 4 months hardly eating, exercising and STILL cannot lose, but feel fine physically. So discouraged and uncomfortable in my body. Exercise has bulked me up, but i hate the look.